Early recommender systems grew out of information retrieval (IR) systems in the early 1970s, and their defining limitation was that they produced the same output for every user. The shift to personalization came when personal computers and widespread internet access made it possible to factor in individual user interaction histories. One of the first systems to rely exclusively on user historical interactions was GroupLens in 1992, which used explicit article ratings. This historical progression matters practically: understanding that modern systems layer multiple techniques on top of that foundation helps teams set realistic expectations about what the technology requires to function well.